Any tips for keeping babies cool outdoors in hot weather?

I don’t take our daughter out in the hot weather. That said, it has never really been warm in the U.K. - we’ve had non stop rain pretty much in the north.

This weekend a friend organised an outdoor bbq to celebrate a 1st birthday party for their child. It’s in an outdoor nature park that’s allows bbqs. We heard on news there will be a heatwave at 31 degrees. I won’t be staying long, they are wanting us to go all day but will be too warm for our child as she won’t be used to the heat.

Are there any tips for what we could do to make it comfortable for her in the duration we are there. We’re taking a parasol for shade, but I’m worried and the parents that organised it don’t seem to think it’ll be a problem to spend the whole day out in 31 degree heat with babies.